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  • TI Thinks Resolved

LSF0108: LSF0108: IBIS model selection

Prodigy 120 points

Replies: 9

Views: 258

Part Number: LSF0108

Hi,

I am using LSF0108 as a level shift between 1.8V and 3.3V, when doing the SI simulation, which model should I use in the IBIS model? The IBIS specifies different model for different VCC, but I have VCCA as 1.8V and VCCB as 3.3V, so which one should I use? Should I use one model for 1.8V to 3.3V conversion and the other model for 3.3V to 1.8V conversion?

|******************************************************************************
| Model LSF0101_IO_S
|******************************************************************************
|
[Model Selector] LSF0101_IO_S
|
LSF0101_IO_50A_S 5 volt Vcc 
LSF0101_IO_33_S 3.3 volt Vcc 
LSF0101_IO_25_S 2.5 volt Vcc 
LSF0101_IO_18_S 1.8 volt Vcc 
LSF0101_IO_12A_S 1.2 volt Vcc

  • Hi,

    Yes the IBIS model has issues modeling many of our parts properly. So yes you would have to use separate models to perform those tests.

    Thanks!

    -Karan

  • In reply to Karan Kotadia:

    Hello Karan,

    My question is which model to use?

    Thank you

    Doron 

  • In reply to Doron Darmoni25:

    Hi Doron,

    You will have to use both. Test them individually for input rise and fall times. There is no option to select an auto bidirectional translator in IBIS. You will have to treat it as a unidirectional device when testing. IBIS models are only for testing signal integrity, not the internal logic or tpd.

    Thanks!

    -Karan

  • In reply to Karan Kotadia:

    Hello Karan,

    i am looking for signal integrity simulation behavior.

    we have a SI issues on the board and try to simulate it and to find the correct approach to resolve.

    in the ibis model it says:

    LSF0101_IO_33_S 3.3 volt Vcc 

    LSF0101_IO_18_S 1.8 volt Vcc 

    BUT Vref A=1.8V & Vref B=3.3V so i don't understand which model to use in this case...

    thank you

    Doron

  • In reply to Doron Darmoni25:

    Hi Doron,

    The way the LSF IBIS model works is that the IO operates like a switch. That is, the model cannot translate 1.8V input to a 3.3V output for example. It can only do 3.3V input to a 3.3V output. So when testing the signal integrity of the output of the LSF device, you will use a 3.3V model and have to provide some 3.3V input source and be able to measure rise and fall times of the output waveform. When you want to test the signal integrity at the input of the device, you will use the 1.8V model with a 1.8V input source and only look at the inputs rise and fall waveforms.

    I hope that made more sense?

    Thanks!

    -Karan

  • In reply to Karan Kotadia:

    Hello Karan,

    thank you for the detailed answer.

    I understand that, but it doesn't make sense - what is the point of the serie switch in that case?

    doron

  • In reply to Doron Darmoni25:

    Karan,

    do you have spice model of the LS0108?

    Doron

  • In reply to Doron Darmoni25:

    Hi Doron,

    We currently do not have a SPICE model on the LSF devices. Can you let me know what you aim to test with the model?

    Thanks!

    -Karan

  • In reply to Karan Kotadia:

    Hi,

    since the ibis doesn't reflects the nalog switch we thought using the spice to simulate it.

    Doron

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